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2024 Day 8 Part 2

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This commit is contained in:
Jeremy Kaplan 2024-12-07 22:00:32 -08:00
commit e0e2c81f6a
2 changed files with 102 additions and 32 deletions
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22
2024/src/aoc.zig
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@ -82,3 +82,25 @@ pub fn parseAll(
return all;
}
pub fn gcd(n: i32, m: i32) i32 {
var a = @abs(n);
var b = @abs(m);
while (b != 0) {
const t = b;
b = a % b;
a = t;
}
return @intCast(a);
}
test "gcd" {
const expectEqual = std.testing.expectEqual;
try expectEqual(2, gcd(2, 4));
try expectEqual(1, gcd(2, 5));
try expectEqual(1, gcd(-2, 3));
try expectEqual(2, gcd(-2, -4));
}

112
2024/src/day08.zig
View file

@ -18,49 +18,29 @@ pub fn main() !void {
var grid = try Grid.parse(allocator, text);
defer grid.deinit();
var nodes = try NodeSet.make(allocator, grid);
defer nodes.deinit();
const stdout_file = std.io.getStdOut().writer();
var bw = std.io.bufferedWriter(stdout_file);
const stdout = bw.writer();
try stdout.print("{d}\n", .{try part1(allocator, grid)});
try stdout.print("{d}\n", .{try part1(allocator, grid, nodes)});
try bw.flush();
try stdout.print("{d}\n", .{try part2(allocator, grid, nodes)});
try bw.flush();
}
fn part1(allocator: Allocator, grid: Grid) !u64 {
var nodes = std.AutoHashMap(u8, aoc.AutoHashSet(Pos)).init(allocator);
defer nodes.deinit();
defer {
var it = nodes.valueIterator();
while (it.next()) |v| {
v.deinit();
}
}
{
var it = grid.iterator();
while (it.next()) |mapEntry| {
const pos = mapEntry.key_ptr.*;
const id = mapEntry.value_ptr.*;
if (id == '.') {
continue;
}
var nodeEntry = try nodes.getOrPut(id);
if (!nodeEntry.found_existing) {
nodeEntry.value_ptr.* = aoc.AutoHashSet(Pos).init(allocator);
}
try nodeEntry.value_ptr.put(pos);
}
}
fn part1(allocator: Allocator, grid: Grid, nodes: NodeSet) !u64 {
var antinodes = aoc.AutoHashSet(Pos).init(allocator);
defer antinodes.deinit();
var it = nodes.valueIterator();
while (it.next()) |nodeSet| {
var aa = nodeSet.iterator();
var it = nodes.map.valueIterator();
while (it.next()) |positions| {
var aa = positions.iterator();
while (aa.next()) |a| {
var bb = nodeSet.iterator();
var bb = positions.iterator();
while (bb.next()) |b| {
if (a == b) {
continue;
@ -81,6 +61,32 @@ fn part1(allocator: Allocator, grid: Grid) !u64 {
return antinodes.count();
}
fn part2(allocator: Allocator, grid: Grid, nodes: NodeSet) !u64 {
var antinodes = aoc.AutoHashSet(Pos).init(allocator);
defer antinodes.deinit();
var it = nodes.map.valueIterator();
while (it.next()) |positions| {
var aa = positions.iterator();
while (aa.next()) |a| {
var bb = positions.iterator();
while (bb.next()) |b| {
if (a == b) {
continue;
}
const d = a.distance(b.*).unit();
var pos = a.*;
while (grid.inBounds(pos)) : (pos = pos.add(d)) {
try antinodes.put(pos);
}
}
}
}
return antinodes.count();
}
const Pos = struct {
r: i32,
c: i32,
@ -112,6 +118,15 @@ const Pos = struct {
const Delta = struct {
dr: i32,
dc: i32,
fn unit(self: Delta) Delta {
const scale = aoc.gcd(self.dr, self.dc);
return .{
.dr = @divExact(self.dr, scale),
.dc = @divExact(self.dc, scale),
};
}
};
const Grid = struct {
@ -157,3 +172,36 @@ const Grid = struct {
0 <= pos.c and pos.c <= self.max.c;
}
};
const NodeSet = struct {
map: std.AutoHashMap(u8, aoc.AutoHashSet(Pos)),
fn make(allocator: Allocator, grid: Grid) !NodeSet {
var map = std.AutoHashMap(u8, aoc.AutoHashSet(Pos)).init(allocator);
var it = grid.iterator();
while (it.next()) |mapEntry| {
const pos = mapEntry.key_ptr.*;
const id = mapEntry.value_ptr.*;
if (id == '.') {
continue;
}
var nodeEntry = try map.getOrPut(id);
if (!nodeEntry.found_existing) {
nodeEntry.value_ptr.* = aoc.AutoHashSet(Pos).init(allocator);
}
try nodeEntry.value_ptr.put(pos);
}
return .{ .map = map };
}
fn deinit(self: *NodeSet) void {
var it = self.map.valueIterator();
while (it.next()) |v| {
v.deinit();
}
self.map.deinit();
}
};